django.db.utils.IntegrityError：（1062，键“ slug”的“重复条目””）

Question

我试图遵循tangowithdjango的书，必须添加一个子弹来更新类别表。但是，尝试迁移数据库后出现错误。

http://www.tangowithdjango.com/book17/chapters/models_templates.html#creating-
a-details-
page

我没有提供该Slug的默认值，因此Django要求我提供一个默认值，并按书中的指示输入。

值得注意的是，与其使用原始书籍中的sqlite，不如使用MySQL。

models.py
from django.db import models
from django.template.defaultfilters import slugify

# Create your models here.
class Category(models.Model):
      name = models.CharField(max_length=128, unique=True)
      views = models.IntegerField(default=0)
      likes = models.IntegerField(default=0)
      slug = models.SlugField(unique=True)

      def save(self, *args, **kwargs):
              self.slug = slugify(self.name)
              super(Category, self).save(*args, **kwargs)

       class Meta:
              verbose_name_plural = "Categories"

       def __unicode__(self):
              return self.name

class Page(models.Model):
        category = models.ForeignKey(Category)
        title = models.CharField(max_length=128)
        url = models.URLField()
        views = models.IntegerField(default=0)

        def __unicode__(self):
                return self.title

命令提示符

sudo python manage.py migrate       
Operations to perform:
   Apply all migrations: admin, rango, contenttypes, auth, sessions
Running migrations:
  Applying rango.0003_category_slug...Traceback (most recent call last):
  File "manage.py", line 10, in <module>
    execute_from_command_line(sys.argv)
  File "/usr/local/lib/python2.7/dist-packages/django/core/management/__init__.py", line 385, in  execute_from_command_line
utility.execute()
 File "/usr/local/lib/python2.7/dist-packages/django/core/management/__init__.py", line 377, in execute
self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/usr/local/lib/python2.7/dist-packages/django/core/management/base.py", line 288, in run_from_argv
self.execute(*args, **options.__dict__)
  File "/usr/local/lib/python2.7/dist-packages/django/core/management/base.py", line 338, in execute
output = self.handle(*args, **options)
  File "/usr/local/lib/python2.7/dist-packages/django/core/management/commands/migrate.py", line 160, in handle
executor.migrate(targets, plan, fake=options.get("fake", False))
  File "/usr/local/lib/python2.7/dist-packages/django/db/migrations/executor.py", line 63, in migrate
self.apply_migration(migration, fake=fake)
  File "/usr/local/lib/python2.7/dist-packages/django/db/migrations/executor.py", line 97, in apply_migration
migration.apply(project_state, schema_editor)
  File "/usr/local/lib/python2.7/dist-packages/django/db/migrations/migration.py", line 107, in apply
operation.database_forwards(self.app_label, schema_editor, project_state, new_state)
  File "/usr/local/lib/python2.7/dist-packages/django/db/migrations/operations/fields.py", line 37, in database_forwards
field,
  File "/usr/local/lib/python2.7/dist-packages/django/db/backends/mysql/schema.py", line 42, in add_field
super(DatabaseSchemaEditor, self).add_field(model, field)
  File "/usr/local/lib/python2.7/dist-packages/django/db/backends/schema.py", line 411, in add_field
self.execute(sql, params)
  File "/usr/local/lib/python2.7/dist-packages/django/db/backends/schema.py", line 98, in execute
cursor.execute(sql, params)
  File "/usr/local/lib/python2.7/dist-packages/django/db/backends/utils.py", line 81, in execute
return super(CursorDebugWrapper, self).execute(sql, params)
  File "/usr/local/lib/python2.7/dist-packages/django/db/backends/utils.py", line 65, in execute
return self.cursor.execute(sql, params)
  File "/usr/local/lib/python2.7/dist-packages/django/db/utils.py", line 94, in __exit__
six.reraise(dj_exc_type, dj_exc_value, traceback)
  File "/usr/local/lib/python2.7/dist-packages/django/db/backends/utils.py", line 65, in execute
return self.cursor.execute(sql, params)
  File "/usr/local/lib/python2.7/dist-packages/django/db/backends/mysql/base.py", line 128, in execute
return self.cursor.execute(query, args)
  File "/usr/local/lib/python2.7/dist-packages/MySQLdb/cursors.py", line 205, in execute
self.errorhandler(self, exc, value)
  File "/usr/local/lib/python2.7/dist-packages/MySQLdb/connections.py", line 36, in defaulterrorhandler
raise errorclass, errorvalue
django.db.utils.IntegrityError: (1062, "Duplicate entry '' for key 'slug'")

Answer 1

让我们逐步分析它：

1. 您要添加slug带有的字段unique = True，这意味着：每个记录必须具有不同的值，而在同一记录中不能有两个记录具有相同的值slug
2. 您正在创建迁移：django要求您提供数据库中已经存在的字段的默认值，因此您提供了“（空字符串）作为该值。
3. 现在，django正在尝试迁移您的数据库。在数据库中，我们至少有2条记录
4. 迁移第一个记录，用空字符串填充子弹列。很好，因为没有其他记录在slug字段中有空字符串
5. 迁移第二条记录，用空字符串填充子弹列。失败，因为第一个记录在slug字段中已经有空字符串。引发异常，迁移中止。

这就是您的迁移失败的原因。您要做的就是编辑迁移，复制migrations.AlterField操作两次，在第一个操作中删除unique =
True。在这migrations.RunPython两次操作之间，您应该放入operation并在其中提供2个参数：generate_slugs和migrations.RunPython.noop。

现在，您必须在迁移函数内部创建BEFORE迁移类之前，将该函数命名generate_slugs。函数应带有2个参数：apps和schema_editor。在您的函数中放在第一行：

Category = apps.get_model('your_app_name', 'Category')

现在用于Category.objects.all()循环所有记录并为每个记录提供唯一的记录。